FDA warns about PML risk with Seattle Genetics' Adcetris

Seattle Genetics has suffered a setback on the news that US regulators have called for a boxed warning on the lymphoma drug Adcetris amid concerns of a link to a rare but potentially fatal brain infection.

The US Food and Drug Administration said the warning needs to be added to the label after two additional cases of progressive multifocal leukoencephalopathy were reported with Adcetris (brentuximab vedotin). At the time of the drug's approval in August 2011, one case of PML was described in the warnings and precautions section of the label.

In addition, a new contraindication warning against use of Adcetris with the cancer drug bleomycin due to increased risk of lung toxicity has been added to the drug label.

Adcetris is a CD30-directed antibody-drug conjugate used to treat Hodgkin lymphoma and a rare disease known as systemic anaplastic large cell lymphoma. It was the first drug to be approved by the FDA for Hodgkin in more than 30 years and since August, about 2,000 patients worldwide have received treatment with the drug.

The FDA granted accelerated approval to Adcetris, for which Takeda holds the rights outside North America. This means Seattle Genetics has to conduct follow-up studies to confirm the effectiveness and safety of the treatment.

By developing these agreed-upon label updates with the FDA,Seattle Genetics' medical officer Thomas Reynolds said "we aim to heighten awareness among healthcare professionals". He added that although PML in lymphoma patients "can be caused by factors such as underlying disease and prior therapies that affect the immune system, a contributory role of Adcetris cannot be excluded".

The company's stock ended Friday down 4.3% to $17.65 but analysts believe investors should not worry too much. Jason Kantor at RBC Capital Markets issued a research note saying that the warning does not represent any serious commercial risk and "we would use any weakness from [the] announcement as a buying opportunity".